Magnetic and optical media are widely employed in various information storage applications, particularly in the computer industry for information recording and retrieval purposes. A magnetic medium as used in computer-related application, comprises a non-magnetic disk-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, together with a plurality of thin film layers constituting the medium. The additional layers can include, a plating layer, e.g., of amorphous nickel-phosphorus (Ni-P); a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr-V); a magnetic layer, e.g., of a cobalt (Co)-based alloy; and a protective overcoat layer, typically of a carbon (C)-based material, e.g., diamond-like carbon (“DLC”) having good tribological properties. Optical media can include a substrate together with operational layers, such as a reflective layer; e.g., of a metal or metal alloy; one or more rare-earth thermo-magnetic (RE-TM) alloy layers; one or more transparent dielectric layers; and a protective overcoat layer, e.g., a DLC layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Magnetic and optical media are typically lubricated with a thin film comprised of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear and provide resistance to corrosion of any metal layers on the media. The application of the protective overcoat and lubricant are important for high durability and reliability of thin film recording media.
Fluoropolyether lubricants are of particular interest in lubricating recording media. These lubricants are suited to form lubricant topcoats on recording media because of their chemical inertness, low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most typically used in forming topcoat lubricants on recording media.
Liquid lubrication of the disk surface encounters several problems, however, which limit its effectiveness in rotating storage media. For example, it is well known that non-bonded lubricants will spin off a thin film disk with a carbon overcoat. Typically, PFPE lubricants do not have a retention means so that when the disk rotates, the lubricant tends to spins off the disk. The depletion of the lubricant from the disk surface tends to increase friction between the disk and the read/write head.
A number of references disclose bonding lubricants to recording media with the use of WV radiation. For example, Lin et al., in U.S. Pat. No. 5,0303,478, teach bonding a lubricant to a carbon overcoat by irradiating the lubricant with UV radiation in a selected intensity and frequency range of 185-254 mm. Tian et al. disclose that far-UV irradiation treatment can be used to obtain bonded lubricants on magnetic recording disk surfaces. See e.g., Tian et al., “Tribological Characteristics of Liquid Lubricant on Magnetic Disks Treated By Far-UV Radiation” J. Tribology, Vol. 115, pp. 400-405 (1993).
In studying the mechanisms of UV bonding of perfluoropolyether lubricants, Vurens et al. teach that photoelectronic emission from the substrate is the cause of bonding of the lubricant. See, e.g., Vurens et al. “The Mechanism of Ultraviolet Bonding of Perfluoropolyether Lubricants” IEEE Transactions on Magnetics, Vol. 29, pp. 282-285 (1993). Vurens et al. teach that illumination with 185 nm UV light renders a lubricant film bonded to a substrate, while illumination with 254 nm light does not result in the formation of such a bonded film on certain substrates, such as amorphous carbon, silica and gold. It is believed, however, that the prior art has not recognized the advantages of the present invention.
Accordingly, a continuing need exists in the art for an improved lubricated recording medium. In particular there exists a need for an efficient, cost-effective method of manufacturing a recording medium with a lubricant topcoat exhibiting improved tribological performance and fly-stiction.